Collison course fire control system



March 24, 1959 E. E. MILLER I 2,379,502

COLLISION COURSE FIRE CONTROL SYSTEM Filed Jan. e, 1946 2 Sheets-Sheetil2 Vt E AE:FF RKD A F i m lk ANTENNA INDICATOR iflfltfi' GENERATOR 74 761 I '77 f f I 7 GYRQ PRECESS a CQMPUTOR i R, vc At A v NETIC MATERIAL 3230 FIG. 3 37 3| INVENTOR EDWARD E. MILLER v33 BY W ATTORNEY March24,1959 E. E. MILLER COLLISION COURSE FIRE CONTROL SYSTEM Filed Jan. 8,1946 2 Sheets-Sheet 2 FIG. 45

FIG. 4A

FIG. 4D I VOLTAGE OUTPUT AZIMUTH E TOC CLY EE T TV ENOW DE INVENTOREDWARD E. MILLER ATTORNEY COLLISION COURSE FIRE CONTROL SYSTEM Edward E.Miller, Medford, Mass., assignor, by mesne assignments, to the UnitedStates of America as represented by the Secretary of the NavyApplication January 8, 1946, Serial No. 639,896 7 Claims. (Cl. 343-7)This invention relates to projectile laying systems and morespecifically to the type for laying a projectile, such as a torpedo, ata moving target from a moving craft, such as a PT-boat.

A common firing technique and the one concerned in this invention isthat employing the collision course principle, wherein the attackingcraft places itself on such a course that, should the target andattacking vessels continue on their respective courses and maintaintheir velocities, the two vessels would collide. The collision courseprinciple is employed because it ofiers to the attacking vessel thenecessary velocity and azimuth heading information of the target vesseland because the collision course condition is one that is easilyrecognized.

Heretofore an attacking vessel got on a collision course by'making aseries of estimated course corrections, but this technique is timeconsuming requiring a long tracking time for a given degree of accuracy.The present invention describes a system which can place an attackingvessel on a collision course with a single correction in .the' azimuthheading of the attacking craft. The system can be adapted to both radarand visual tracking of the target vessel.

A specific object of this invention is to provide apparatus for rapidlyand accurately laying a projectile at a moving target from a movingcraft.

Another object is to place an attacking craft on a collision course witha target vessel by means of a single adjustment in the azimuth headingof the attacking craft.

'Another object is to provide projectile laying apparatus whoseoperation is totally independent of the pitch, roll, or yaw of thevessel on which it is mounted.

Another object is to provide projectile laying apparatus havingincorporated therein means for indicating when two coaxial and abutting,mechanically independent shafts are in proper alignment.

Another object is to provide a projectile laying system.

having incorporated therein means for providing a stabilized azimuthmarker on a radar indicator scope.

A further object is to provide a projectile laying apparatus havingincorporated therein a simple computer for turning one shaft by anamount mathematically related to the motion of a second shaft.

A further object is to provide a projectile laying system which may beoperated from either radar or optical data.

Another object is to provide a radar projectile laying system which isoperative with either a stabilized or an unstabilized trackingindicator. 7

To achieve these and other objects, apparatus is employed'which isdescribed in detail in the following specification and shown in theaccompanying figures, of which:

Fig.1 is an illustration of the collision course principle and themanner in which the present invention is adapted to this firingtechnique;

'Fig. 2 is a block diagram of the system of the present,

invention;

Fig. 3 is a perspective drawing showing schematically v Theapproximation improves as the angle Act diminishes, and AB correctionsof greater precision can be made ifthe correlation between the radar,the azimuth marker,

and the gyro of the present invention;

Fig. 4A is a graph of the detected output of the azimuth marker of thepresent invention;

Fig. 4B shows a plan position indicator, or P.P.I., with the azimuthreference lines placed thereon; Fig. 4C is a'circuit which may beemployed to produce the azimuth reference lines shown in Fig. 4B.

Fig. 4D shows the waveform of the output of the cirwill of Fig. 4C.

Fig. 5 shows the resistance network computer associated with thegyro-precess means and the ship steering mechanism.

In the accompanying drawings and more specifically in Fig. 1 are shownan attacking craft 11 moving with a constant velocity C and a targetvessel 12 traveling at a constant velocity V initially displaced fromone another In a time At, the attacking craft 11' travels to a position13, and the target vessel 12 moves up to a position 14. From the figureit can be seen that by a range R the two vessels shown are not on acollision course and that the attacking vessel 11 will fall astern ofthe target vessel 12. The condition which indicates to the attackingvessel 11 that the two vessels 11 and'l2 are not on af collision courseis that the original relative azimuth angle 1 '0 changes in a time At byan angular amount Act. If the two vessels 11 and 12 were on a collisioncourse, the

relative azimuth angle 0 would remain unchanged as the two vesselsapproach one another.

To get on the proper collision course at the time |t=At the attackingvessel 11 must alter its course by an angle A 8, and the presentinvention is based upon the fact that 1 A 8 is determined from the knownquantities, range R interval. At, and the easily 5 measurable angle Au.These quantities are related by the velocity V and time approximatemathematical expression V At necessary during the course of attack.

Considering the use of a search radar system with a plan positionindicator for giving position information of the target vessel 12,initial range R can be measured' directly on the indicator presentation15 of Fig. 1. The

knowledge of own velocity V is obvious,and the time interval At mayconveniently be chosen as the time for an integral number of completerotations of the radar antenna. The angle Act can be measured if anazimuth reference line is maintained. Such an azimuth reference isprovided by a gyro which is initially uncaged with its axis pointingdirectly at the target vessel and which presents on the radar azimuthindicator 15 a stable azimuth marker con--- sisting of two adjacentradial lines 19. The oscilloscope radar presentation 15 of Fig. lshowsthe initial tracking condition with the radar echo 17 at a range Rbracketed by the two radial lines 19 of the gyro stable azimuth marker.Indicator picture 16 at a time t=At shows Au as the easilymeasurableangle between the center line 20 of the stable azimuth markers19 and the radar echo 18. To solve for the azimuth heading correctionangle A3 which is ultimately desired, the gyro originally mentioned isprecessed sothat the stable azimuth marker line 20 controlled thereby isbrought into azimuth alignment with= By so processing the the radar echo18 at time t=At. gyro,-the rotation axis thereof is againpointeddirectly computer comes the angle At? which may either go to ahelmsman indicator on the attacking vessel or serve to turn theattacking craft directly.

After turning the attacking craft 11 through an angle AB, the attackingand target vessels 11 and 12lie on relative courses which will causethem to collide at point 21. An indication that the two are on collisioncourse is that the new relative azimuth angle 11: remains constant asthe two vessels approach one another. This condition is indicated onindicator picture 22 by the successive radar echoes of the target vesselfalling within the stable azimuth marker of that indicator. It will benoticed that the indicator shown in Fig. 1 is unstabilized, with the topof the scope representing dead ahead.

Before the two vessels 11 and 12 reach the collision point 21, theattacking craft 11, which in the particular situation considered ismaking a torpedo attack, swerves in'toward the targetvessel by an angledeterminedby the relative velocity of the torpedo and the attackingvessel 11, and releases its projectile 23. The final point of impact ofthe torpedo with the target vessel is indicated by point 24. Theapparatus brought into use after the attacking and target vessels are ona collision course is not a part of the present invention.

'Refer now to Fig. 2 which is a block diagram. A search radar system 70is employed having an antenna 71 that is sufficiently directive toprovide accurate azimuth information and an indicator 72 for presentingboth range and azimuth information. Thegyro 73 shown, having anassociated precess mechanism 74, provides the desired stabilizedreference azimuth information. Both the antenna 71 and one of the gyrosupporting frames or gimbals are coupled to an azimuth marker generator75. It is the latter. unit which places the-aforementioned stableazimuth lines on the radar indicator 72. A computer 76 has its operationdependent on R V At, and A0: in-

-- formation and solves for the azimuth heading correction angle At?which is finally transmitted to the shipsstecring mechanism 77. Thearrows on Fig. 2 indicate the direction of flow of information.

Refer now to Fig. 3, which shows schematically the correlation betweenthe radar, the gyro, the azimuth marker generator and the deck of theship itself. A radar system having an antenna 25 rotatable about theaxis AA of shaft 26 is shown with its beam pattern having a.plane ofmaximum radiation intensity which contains axis AA. Mounted also onshaft 26 or synchro-coupled thereto is the U-shaped bar 29 which is madeof magnetic material and which lies in the first plane defined.

A gyroscope having a rotor 30 is mounted on two supports or gimbals 31and 32, the outer gimbal 32 being mounted on the deck plane 33 of theship and being rotatable about an axis AA which is perpendicular to the'deck plane 33. The gyro thus has complete freedom of motion, allowingthe rotor axis B--B to be positioned as desired. Rigidly attached to theouter gimbal 32 of thegyro is magnetic coupling bar 34 which is solocated that the end of the first coupling bar 29 can sweep closely byand form a closed magnetic loop or circuit without any friction forcesbeing transmitted by the driven bar 29 to upset the gyro alignment.Primary and secondary coils 35 and 36 are wound on coupling bar 29, andit can be seen that with an alternating signal on the primary winding35, a maximum output signal will appear at the secondary winding 36 whenthe magnetic bars 29 and 34 are in such rotational alignment that theyform a closed magnetic circuit. It is this output signal that isemployed to produce the stable azimuth marker on the radar indicator, aswill later be discussed.

It should be emphasized that Fig. 3 is' a schematic representation ofapparatus of this invention. In an actual system, all of the componentsmay not conveniently line up on a single reference axis AA, but thisfact does not cause operation of the actual system to deviateappreciably from that of the simplified one shown in Fig. 3.

Supporting member 37 also does not actually exist, but represents all ofthe rigid structure on the ship which holds the various components andtheir associated parts in alignment.

One of the most important features of the system of this invention isthat the coincidence between the gyro stable azimuth marker and thetarget vessel echo on the radar indicator is entirely independent of anyroll, pitch or yaw of the attacking vessel. This aspect of the inventioncan be shown in terms of the structure of the Fig. 3.

The reference axis AA, which is perpendicular to the deck plane 33, andthe gyro axis B--B define a first plane which is perpendicular to thedeck plane and which contains the magnetic bar 34. A second plane isdefined by the axis AA and the radar beam central radiation axis C-C.This plane, also perpendicular to the deck plane, contains a plane ofmaximum radiation intensity of the radar and the magnetic bar 29. By therelated action of magnetic bars 34 and 29, an azimuth marker is placedon the radar P.P.l. scope when these two planes coincide.

In operation, the target by pointing gyro axis the first plane is madeto initially contain B-B directly at the target. For a collision course,it is necessary that the target remains at the same relative azimuthbearing with respect to the attacking craft as the two vessels close.Thus, if the attacking craft is on collision course, the gyro axis B-Bcontinues to point at the target and the first plane contains the targetno matter how much the attacking vessel pitches, rolls, or yaws. Underthis..circumstance, the second plane passes through thelfirst plane andthe target simultaneously and the target radar. echo remains centered onthe P.P.I. azimuth marker regardless of how much the marker swings onthe radar indicator due to the attacking ships instability. Should theattacking vessel be ofi its collision course, however, the relativeazimuth bearing of the target will shift and the first plane will nolonger contain the target. As a result, the second plane will coincidewith the first either before or after the second plane passes throughthe target, and the radar echoes and the azimuth marker will not becoincident on the indicator.

Another way to analyze this stabilization scheme is to consider that thegyro axis B--B and the radar axis 0-0 are both projected perpendicularlydown onto the deck plane. It is these deck projections that are referredto the indicators by the antenna synchro and the magnetic coupling bar.By so referring both the 8-8 and C--C axes to the same reference plane,motion of this plane does not affect the relation between the twoprojected axes.

The manner in which the double line, stable azimuth marker is formed bythe output signal of the magnetic coupling structure previouslydescribed is shown in Figs. 4A, 4B, 4C and 4D. Fig. 4A shows thedetected envelope 40 of the alternating signal which is produced on thesecondary coupling winding 36 of Fig. 3 as the two magnetic couplingbars 29 and 34 of that figure sweep past and couple with one another.From this envelope, it is desired to produce two pulses, symmetricallyrelated to the peak of the curve, which may be used to intensify theradar indicator beam. On the P.P.I. cathode ray indicator, asillustrated in Fig. 4B, two radial lines 45 and 46 are formed and theseare symmetrically disposed about an axis 47 which corresponds to thecenter line 43 of Fig. 4A.

One of a number of circuits which may be used for producing twointensifier pulses at points 41 and 42 of the curve of Fig. 4A is shownin Fig. 4C. The detected prising resistors 52 stages 50 and 51.

far he'yond'cut off" '(biasing means not shown), 's'tartsto conduct whenits grid voltage rises to the value 54 of Fig. 4A. Stage 51 isquiescently held in saturation by As'the result of this action, theoutput voltage has a sharp rise 56.

Stage 51 finally cuts oli, with the conduction of stage" 50 stillincreasing, and theoutput voltage'falls (57) to the level 58 where stage50 is finally saturated. The circuit of Fig. 4C has 'thus been flippedover, producing a large voltage pulse 59 at the point 41 of Fig. 4A. Asimilar pulse 60 is produced at the point 42 of Fig. 4A- as the inputvoltage to stage 50 falls to its initial value. After inverting andclipping the wave of Fig. 4D at some level 61, the two resulting pulsesare placed directly on the intensifier grid of the radar indicatorcathode ray tube (P.P.I.) Any number of other types of circuits may beadapted by those skilled in the art to perform-this pulse generatingfunction.

Referring now to Fig. 5, the computer for solving the relation betweenthe azimuth deviation angle Au and the azimuth heading correction anglefor collision course AB is shown. This apparatus comprises a AOLgyroprecess means 74'having an input resistance R and adapted to precessthe gyro of the system at a rate proportional to the voltage which saidprecess means receives, a constant speed, rapid start-stop, reversingmotor 79 which directs AB information to the turning mechanism of theattacking craft, and a control. box 76 having included'therein a switchfor operating the A motor 79 in either direction and for operating thegyroprecess means 74, and a resistive network for controlling thevoltage,vand thus the rate of precession, of the Au gyrmrecess-mechanism 74.

As previously discussed, the equation which relates Ag? and Act is SinceAe is introduced by a constant rate device (motor 79);. and AG by avariable rate device (gyro-precess means 74), and since the same switchis used for on and off control of both rate devices, the relationbetween the Ace angle of rotation A5 and the angle of precess Am can: becontrolled entirely by adjustment of the variable gyro-..

led to a fictitious +12 voltage point. As a result, resistors 65, 66 and67 can be effectively placed across a +12 or 12 volt supply by switch63.

Computation is done by the hand set taps on resistors 66, 67 and byvariable resistor 68, and to correlate adjustment of these with thecomputation which they perform, it must be noted that increasing thecontrol voltage to the A0: gyro-precess means 74, increases the rate ofprecess thereof and thus decreases the angle Afi generated by theconstant speed motor 79. Thus increasing the I operation is based onHowever, it will be obvioust'o those; skilled in the art that thetechnique involved might easily be adapted to claim is: p

- 1. Apparatus for laying a projectile at a moving tar- R tap onresistor '67 decreasesg'yro-pre'cess rate, while? increasing the At tapon resistor 66 causes an increase in gyro-precess rate. This is all inkeeping with the above equation. Velocity V is introduced to the resistive network by control of the magnitude R of resistance 68. The R andAt resistance controls are linear, while the introduction of V byresistance R; is determined by the equation 1 R4=T/:R3 R being the inputresistance of the gyro-precess circuit. The apparatus of the presentinvention has been described with respect to a projectile laying systemWhose the collision course principle.

other types of fire control or navigation and with other than seacraft.Since radar replaces optical systems when darkness, fog, smoke, etc.'make the latter inoperative, it will be obvious that an opticaltracking'meansmightv well be'used under-circumstances favorable theretoin-' stead of the radar described above. The scope of this inventionshould further be interpreted to encompass the "use of combined opticaland radar systems with'one serving as a check upon the-other.Furthermore the simple technique of fully stabilizing the trackingapparame of the present invention against ships pitch, roll, and

yaw is adaptable to any number of other types of systerns requiringsimilar stabilization. g

The invention described in the foregoing specification need not belimited to the details shown, whichare considered to 'beillustrativeofone form the invention may take. What I desire to secureby Letters Patent and get from a moving craft; said apparatus comprisinga radio echo detection and ranging system including a rotary scanningantenna and a range-azimuth indicator, aj gyro, precess means forcausing said gyro to precess,

means mechanically coupled to said antenna and said gyro for producing astable azimuth marker on said indicator, acornputer, said computer-beingcoupled to said precess means for controlling the rate at which saidgyro -pre'cesses, and constant speed reversible motor means controlledby said computer for determining an azimuth heading correction anglemathematically related to a' gy o precess angle. i 21 Apparatus r layinga projectile at a moving target from a moving craft, said apparatuscomprising a radioecho detecting and ranging system including a rotaryscanning antenna and a' range-azimuth indicator, a gyro having precessmeans associated therewith, a computer coupled to said precess means forcontrolling the rate at which said gyro is causedto precess,constantspeed reversible motor means controlled by said computer fordetermining an azimuth heading correction angle mathematically relatedto ,agyro precess angle, and means for producing a stable azimuth markeron said indicator, said marker producingmeans including mag neticcoupling bars mounted on 'two shafts respectively representing theazimuthal position of the antenna and the rotor of said gyro, said barsbeing so shaped that they communicate with one another withouttouching'to form an essentially closed magnetic circuit when saidantenna and gyro rotor are in a predetermined azimuthal relationshipmeans for inducing a magnetic field in said bars, and a signal coilassociated with one of said bars for conveying an output signal to saidindicator.

3. In a fire control system of the type wherein an attacking craftmaneuvers to close on a moving target along a collision course, thecombination of a radio .pulse echo detecting and ranging system carriedby said nave-mos 1 search pulses and receives echo pulses reflected fromire-- mote target anda synchronized plan position indicator fordisplaying the azimuthandrange of targets so detected, I

means for producing on the face'of said plan position indicator apair'of angularly dis'posed, illuminated-radial traces during eachcycleof rotation of said directional 1 I antenna, said radial traces defininga sector on said, plan position indicator Which delineates apredetermined I search area covered by said system, means forinitially Ilocating said sector so that it is centrallydisposedabout therepresentation on the plan position indicator of the.

tating directional "antenna: which periodically radiates, search pulsesand receives echo pulsesreflected from ,re-t

mote targets, and a synchronized plan position indicator directionalantenna, said radial traces defining a sector; on said planpositionindicator which delineates a predetermined search area covered by saidsystemmeans- 1 for initially adjusting the time of occurrence of saidspace I I azimuth bearing-of said moving target, means operative I tionthrough which'said sector shifts.

targets and a synhcronized planposition indicator for displaying theazimuth and range of targets so detected,

a-generator for producing a pair of spaced pulses during each cycle ofrotation ofsaid directionalantenna, means for supplying said spacedpulses to the intensity control electrode of said plaiifpositionindicator whereby apair,

of angular'ly' disposed radial traces are produced on the face of saidplan position indicator,said radialtraces de- I fining a sector on said.indicator which corresponds to a predetermined amount of search area,means for initially setting the time of occurrenceof said space pulseswhere I by said sector is symmetrically disposed about a first azi:

i inuth bearing on said plan position indicator of said moving targegandmeans for varying at a given time later, the time of occurrence of saidpair of pulses so that said I I a' predetermined time later. forshifting the location of said 'sectorsothatit 'isagain'centrally'disposed about the. representation of the azimuth bearing of saidmovingtarget, and means ,for correcting the steering of said at,,tacking'craft in accordance withthe'amount and direc- I 7 motor fordriving the steering mechanism of the attacksector progressively shiftsits location until it reaches a position on said .plan positionindicator at which it again is symmetrically disposed about a secondazimuth bearing of said moving target, the angular distance throughwhich said sector shifts providing a measure of the amount of steeringcorrection that is needed to bring said attacking craft on a collisioncourse to said moving target.

5. In a firev control system of the type wherein an atfor displaying theazimuth and, range of'targetsso de-- 'tected, means for producing on;the face of said plan I position indicator a pair of angularly disposed,illuminated radial "traces duringeach cycle of rotation of saidpnl'sesduring each cycle of rotation of said directional antenna so thatsaid sector is symmetricallydisposed aboutthe azimuth bearing on saidplanposition indicatorof said moving target, and'means vfor subsequentlyvarying the time of occurrence of saidpairsof. pulses during successivecycles of rotation of said directional an-' I I tenna until said sectorshifts to a'position at which it again is symmetrically disposed aboutthe ,latest azimuth bearing' of said moving target, the angulardistance/through I L which said sectorshifts identifyingtheazimuthheading correction angle for the collision course.

I '6. In a system as defined in claim 5, means for regulating the rate,atwhich said means for changing the time of occurrence of. said pairs ofpulses functions, whereby the time required to shift the position ofsaid sector: is controllable.v I

7. In a system as defined in claim 5, a constant speed ing craft, andmeanstor' energizing said motor for a length of time'equal to thatrequired for said selector v to shift its position and in a directioncorresponding to I that 'in whichsaid sector moves on said plan positionindicator.

I I j References Cited in the'file of thispatent I 1 UNITED STATES,PATBNTSI 2,369,622

*Toulon Feb. 13,. 1945 I 2,420,016 1 Sanders May 6, 1947 2,420,017"Sanders May 6, 1947 2,422,697 Meacham June 24, 1947 2,434,813 SandersJan; 20, 1948 2,437,286 Witt Mar. 9, 1948 2,447,728 Bartholy Aug. 24,1948 2,472,129 Streeter June 7, 1949 2,476,746 Libman July'19, 19492,488,448 Townes Nov. 15, 1949 2,510,129 Moore June 26, 1950 2,521,726Ivall Sept. 12, 1950 A 2,547,363 Bishop Apr. 3, 1951 2,552,172 Hawes May8, 1951 t

